One person dies every 30 minutes in the U.S. as a consequence of head and neck cancer. Solid tumor growth is dependent on the ability of tumor cells to recruit and sustain their own microvascular network. Therefore, targeted disruption of the tumor vasculature might be beneficial for the treatment of patients with oral cancer. The broad long-term goals of this research are to understand the biology of microvessel regression and to develop antiangiogenic strategies for oral cancer. The objectives of this application are to study the process of caspase mediated disruption of human microvessels in vitro and in vivo, and to examine the effect of the disruption of the tumor neovascular network on oral tumor growth. Dimerization of caspase-9, an apical protease of the apoptotic pathway, activates an irreversible signaling pathway that results in cell death. To perform the studies proposed here. An inducible artificial death switch (iCapase-9) has been as engineered and characterized; it consisted of the catalytic domain of caspase-9 fused to an FKBP-based dimerizer domain. Microvascular endothelial cells stably transduced with iCaspase-9 will be plated in collagen matrices to study molecular mechanisms of capillary tube disruption in vitro. Human microvessels will be engineered in immunodeficient mice with endothelial cells expressing iCaspase-9 to study the biology of microvessel regression in vivo. There are also plans to design and characterize a targeted adenoviral vector to deliver iCaspase-9 specifically to the tumor endothelium. Tumor neovascular endothelial cells express specific markers (alpha vBeta2 and KDR), which are expressed in low levels, or not expressed by endothelial cells of mature blood vessels. The approach will target the adenoviruses to tumor neovessels by: 1) enhancing the tropism of the vector with the incorporation of the RGD-4C peptide (shown to bind to alpha v Beta3 and to home specifically to tumor neovessels into the adenoviral fiber protein; and 2) by driving the expression of iCaspase-9 with domains of the promoter and enhancer of KDR (shown to be preferentially expressed in tumor neovessels). This research will enhance the understanding of the biology of neovascular regression, and will investigate a novel anti-angiogenic strategy based on targeted delivery and controlled activation of a pro-apoptotic caspase in the endothelium of oral tumors.